This invention relates a secondary alkaline battery having a zinc negative electrode and a microporous membrane separator and more particularly to a nickel-zinc battery containing same. Nickel/zinc batteries are one of the more promising batteries for electrical cars and various military vehicles, the advantages including a relatively high energy density and constant voltage output. In addition, a zinc anode containing cell or battery has other advantages, for example, a high energy to weight ratio and a low price. There are problems associated with the use of zinc anodes, particularly regarding the life of the secondary cell or battery, all of which result from the special properties of zinc in an alkaline electrolyte. Typically, electrolytes used in these batteries are hydroxides and particularly alkali metal hydroxides which may be saturated with zinc oxide.
The zinc anode is a so-called dissoluble electrode, which during the discharge reaction forms products soluble in the electrolyte. These products leave the anode mainly as zincate ions which then may react further in the electrolyte. Zincate ions then form zinc oxide which has a much lower solubility in the electrolyte than the zincate ions. Zinc oxide thereafter may precipitate as a solid. The main reactions during the discharge of the zinc electrode and the precipitation of the zinc oxide are the following: EQU Zn+4 OH.sup.- =Zn(OH).sub.4.sup.2- +2e.sup.- EQU Zn(OH).sub.4.sup.2- =ZnO+H.sub.2 O+2OH.sup.-
Other reactions and other types of ions are present, but the above reactions are the dominating reactions and illustrate the main reactions in the secondary cell.
One of the most significant problems with zinc electrodes and accordingly the nickel-zinc battery, results from the redeposition of zinc on the electrodes during the charging process during which time the zinc to a major extent forms zinc dentrites which have a tendency to grow toward the counter electrodes and cause a short circuit in the cell.
Different methods have been tried to solve these problems with the use of a semipermeable membrane between the zinc electrode and the counter electrode being a common configuration in the art. One such method is illustrated in a series patents to von Krusenstierna relating to vibrating the electrodes to avoid the dentrite formation, see U.S. Pat. No. 3,923,550 issued Dec. 2, 1975; U.S. Pat. No. 4,015,053 issued Mar. 29, 1977; U.S. Pat. No. 4,052,541 issued Oct. 4, 1977. Other methods include using different kinds of additives in the electrolyte to prevent dentrite growth on the membrane and electrodes. As reported by von Krusenstierna these attempts have not met with significant success.